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Project 11: "Variable Star Search"
by Barrett Duff
Level: Advanced
Requirements: Filter Wheel, Photometry Software
Objective
This project is an extension of Project 9, for which candidate stars are examined for possible variable status. Such candidate stars are obtained from various sources listed in the references. Results are publishable and can be reported to the Information Bulletin for Variable Stars, and/or to the American Association of Variable Star Observers (AAVSO) for publication.
Background
Variable stars are important clues to the structure and dynamics of the universe as well as stellar evolution. The discovery of new variables and refining or adding data on known variables is an important contribution to the science of astronomy. In the past, most variable stars have been detected by the blink comparison of plates taken of the same portion of the sky at different times. The application of this tedious process has resulted in the identification of thousands of variables but the method is less useful for the remaining, generally dimmer stars. CCD astronomy coupled with powerful new software for tabulating the magnitudes of all stars on an image opens up the possibility of applying statistical analysis to identify the variables and discover the new ones. The Welch-Stetson technique presented in the first reference herein is a good example of how this can be done.
Discussion of Work
Students should select an area of the sky with suspected variables. Older open clusters with red giants are good candidates. Even some of the closer galaxies such as M31 and M33 contain supergiants that can be resolved by the TIE telescope. The New Catalogue of Suspected Variables and AAVSO publications will provide other possibilities. As is the usual case, one should try to pick a target area that lies above 30° N in the East during the early evening of the first scheduled date for observing. In this way the target will be available in the evening sky for two or three months. Take one image early in the on-line session and a second image later in the same session. Using an R or V filter should improve the results. The analysis of reduced data of the two images will point to probable variables which can then be checked against known variables. If you have found a new candidate, images taken during subsequent imaging sessions will confirm the variation in magnitude and eventually yield a light curve and period. Positive results should be reported as soon as they are confirmed by repeated measurements.
References
D.L.
Welch, Discovering Variable Stars, CCD Astronomy, Vol. 3 No. 1, Winter 1996,
p. 14
AAVSO Publications
General Catalog of Variable Stars and the New Catalog of Suspected Variable
Stars; the best source for these two works is via the Internet at:
http://adc.gsfc.nasa.gov/adc_holdings/htm#cat2
(look for catalogs 2139B & 2140 within this site
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